This invention relates to an improved VIB metal-VIII metal carrier catalyst suitable for hydrotreating hydrocarbon stocks.
Hydrotreating refers to the process of hydrodesulfurization, hydrodenitrogenation and demetallization of hydrocarbon feedstocks. This invention is especially directed toward the preparation of a catalytic composite having superior hydrotreating activity for the removal of sulfur and nitrogen in heavy hydrocarbon stocks. Examples of such heavy stocks are total crude oil, crude residua, atmospheric and vacuum gas oils, and cycle oils.
Crude petroleum oil, and heavy hydrocarbon fractions and/or distillates derived from crudes, contain components such as nitrogen, sulfur and metals. These impurities may exist in heteratomic compounds and are often present in relatively large quantities. Such impurities may poison or modify catalysts used in the upgrading of petroleum fractions in reforming or cracking steps. Nitrogen and sulfur are also objectionable because combustion of hydrocarbon fuels containing these impurities releases nitrogen and sulfur oxides. Such by-product gases are noxious, corrosive and present a serious problem in the field of air pollution.
The removal and/or conversion of these impurities is effectively carried out by catalytic hydrotreating, where a feedstock containing sulfur and nitrogen is contacted with a supported catalyst in the presence of hydrogen. Hydrotreating conditions may include a wide range of temperatures, pressures and space velocities as determined by the design of commercial refineries.
Supported catalysts can be generally characterized as comprising metallic components, supported on a refractory inorganic oxide carrier of synthetic or natural original and having a medium to high surface area and a well-developed pore structure. Metallic components having hydrotreating activity may include the metals of Groups VIB and VIII of the Periodic Table.
Numerous disclosures have been made for methods of preparing supported catalyst for hydrotreating. Catalytic metals may be applied to a formed or unformed carrier by one of several impregnation methods known to the art. This is usually followed by forming, if necessary, and by calcination to convert the catalytic metal compounds to oxides.
Several prior art disclosures have been proposed for preparing active hydrotreating catalysts by single impregnation techniques using acid stabilized solutions of the catalytically-active metals.
U.S. Pat. No. 3,232,887 discloses a method of impregnation of catalyst supports, in which the metals impregnating solution is stabilized with an acidic compound. The acidic stabilizer may be organic, e.g., gluconic or citric acid, or inorganic. The preferred acid is phosphoric. The acid stabilized solution contains Group VIB and Group VIII metals where, in the case of phosphoric acid, the phosphorus to Group VIB molar ratio, e.g., P/Mo, ranges from 0.25 to 2.5.
U.S. Pat. No. 3,287,280 discloses a method of preparing a hydrodesulfurization catalyst by impregnating a formed alumina support with a stabilized phosphoric acid solution of molybdenum and nickel salts. The solution contains "at least about 0.2 mole of phosphoric acid per mole of molybdenum metal" and is limited in some claims to a molar ratio of P/Mo of 0.2 to 0.8.
U.S. Pat. Nos. 3,817,873 and 3,755,196 relate to a stable metals solution, a method of preparing the same, a catalyst preparation method using the metals solution, and the resulting catalyst. The metals solution contains molybdenum, nickel and/or cobalt, and an acid containing phosphorous, having a P/Mo molar ratio of 0.1 to 0.25.
U.S. Pat. No.3,840,472 discloses preparation of an impregnating solution where "the promoter solution of the (disclosed) invention consists essentially of molybdic oxide, at least one of the specified Group VIII metal compounds and phosphoric acid dissolved in water". The solution may contain molar ratios of P/Mo in the range 0.065 to 2.5.
In addition to the above single impregnation methods with acid stabilized solutions, the prior art discloses methods of preparing hydrotreating catalysts by multiple impregnations and/or stepwise methods, to incorporate the active metals into the formed or unformed support.
U.S. Pat. No. 3,114,701 discloses a catalytic hydrodenitrification process using a catalyst prepared by multiple impregnations of a formed alumina support with aqueous solutions of nickel nitrate and ammonium molybdate, such that the nickel content on the finished catalyst is in the range of 4-10 percent by weight and the molybdenum metal content on the finished catalyst is in the range of 19-30 percent by weight on the calcined composite.
U.S. Pat. No. 4,097,413 claims the preparation of a desulfurization catalyst by first co-mulling boehmite alumina with an aqueous ammonium molybdate solution, drying the resultant mixture, then co-mulling with a soluble cobalt salt. The mixture is then
U.S. Pat. No. 4,048,115 discloses a stepwise method of preparing a desulfurization catalyst. Column 1, line 58, states that " . . . the present invention relates to a desulfurization catalyst comprising an inorganic oxide carrier material, a Group VIB metal component and a Group VIII metal component wherein said catalyst is prepared by (a) extruding at least 10% of the Group VIII metal component with the inorganic oxide carrier material, and (b) impregnating the resulting extrudate with a sufficient quantity of Group VIB and Group VIII metal components to yield a finished catalyst containing the requisite metallic component content."